The only real disadvantages are that typing is a little slower (I type around 90 WPM but speak around 150 WPM) and that you don't get body language cues in writing. For the sorts of things I am interested in, though, I actually prefer not having body language. Body language makes us try to react to others by guessing their mental states from some subtle changes in their shape. This is problematic for two reasons; first of all, this sort of guessing is inherently imperfect, but more importantly, we tend to be quite heavily influenced by our perceptions of others' reactions. (This makes sense, evolutionarily; it is a way of making us cooperate and preventing us from diverging too much.)
What this means for conversation is that topics are chosen, opinions are suppressed, and minds are changed purely on the basis of our faulty readings of others' opinions. This is especially problematic when talking about abstract ideas because subconscious emotional reaction is an awful predictor of the merit or validity of ideas. The problem is compounded because we are very bad at simply setting aside our reactions, especially in social contexts.
Body language heuristics are obviously good for some things. They help us negotiate relationships, know when others are upset, and interpret ambiguity. But they also give us false impressions and lead to socio-cognitive biases. Furthermore, a large proportion of the benefits of body language come from dealing with problems of face-to-face interaction between primates, meaning that the benefits are less when dealing with textual communication (and especially communication about abstract ideas).
Even small talk over IM seems to be more stimulating to me on average than face-to-face small talk. I have observed this not only in my own interactions but in watching the interactions of others as well. My sample could be biased, because I am obviously a nerd who mostly hangs out with other nerds, but I think I've seen enough "normal" people to make a general statement. Your mileage may vary if you have different tastes in conversation than I do. But if you prefer to talk about the abstract or the complex, or if you try to avoid cognitive biases, then the only way I can imagine face-to-face conversation being generally preferable is if it has a strong instinctive appeal to you.
A lot of people do seem to have this innate preference. The same people often seem to prefer reading on paper than on screens. Some of them say their preference is based off of eye strain--which might even be a reason to prefer speech over text--but for a lot of people the reason seems to be more aesthetic.